An important analog building block, especially in analog signal processing systems, is the variable gain amplifier (xe2x80x9cVGAxe2x80x9d). VGA circuits are necessary components in many signal processing and data acquisition systems which typically include analog-to-digital (xe2x80x9cA/Dxe2x80x9d) converters. The use of a VGA at the front of a data converter, such as an A/D converter, is usually preferred to best utilize the converter""s dynamic input range.
As signal processing speeds continue to rise, the need for continually faster data converters, and therefore also faster VGA""s, arises as well. Unfortunately, typical VGA""s suffer from operating speed and bandwidth limitations due to their circuit design. Further, the operational parameters of such VGA""s are sensitive to process tolerance, temperature and supply voltage variation. This further limits the use of these VGA""s with smaller process and/or lower voltage technologies.
Accordingly, there is a need for a variable gain amplifier which operates at high speed and with a wide bandwidth and with operational parameters that are insensitive to process tolerance, temperature and supply voltage variations.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiments described below relate to a variable gain amplifier (xe2x80x9cVGAxe2x80x9d). The VGA includes at least one signal path gain cell characterized by an open loop architecture and operative to amplify a differential input signal by a first gain according to a gain control signal, and a replica gain cell coupled with the at least one signal path gain cell and a gain input and operative to amplify a first reference signal according to the gain input and generate the gain control signal.
The preferred embodiments further relate to a method of amplifying a signal.
In one embodiment, the method includes applying a gain control value to a replica gain cell corresponding to a selected gain of a signal path gain cell, applying a first reference signal to the replica gain cell to be amplified, equalizing, substantially, the amplified first reference signal to the first reference signal, deriving an adjusted gain control signal based on the equalizing, and applying the adjusted gain control signal to the signal path gain cell to achieve the selected gain.
Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.